1. Field of the Invention
The present invention relates to a method for measuring a Muzzle Velocity of a projectile or the like.
2. Description of the Background Art
Prior art measurement devices and methods use at least one coil pair, which as a rule is located following a muzzle brake of a weapon. The coils here are positioned at a defined distance from one another, wherein the velocity V0 is determined by the measured time the projectile requires to travel the distance defined by the coils.
Such a device is known from CH 691 143 A5. In order to measure the shell velocity of a rapid-firing gun, two sensors are arranged at a distance from one another on a support tube at the muzzle of a gun barrel. These sensors, which respond to changes in a magnetic flux, stand in connection with an analysis electronics unit and have a coil pair consisting of two coils and a closed magnetic circuit. The measured shell velocity, or the fuze timing updated thereby, is then generally communicated to the shell as information before the shell exits the muzzle area.
DE 697 09 291 T2 (EP 0 840 087 B1), which corresponds to U.S. Pat. No. 6,032,568, discloses a means for controlling the initial velocity of a shell. in this context, sensor means are provided that can measure a parameter related to the muzzle velocity. This takes place with the aid of the sensors, located at least in or on the gun muzzle, which can measure an increased pressure in the gun muzzle that arises as a result of the heating of the propellant gases at the gun barrel. Proposed as sensors are strain gauges that are adapted such that they are in contact with the gun muzzle. The expansion of the gun muzzle is measured here. The motion of the projectile and, thus its velocity, is determined from the time difference in detection of the projectile passage by the two individual sensors.
DE 103 52 047 A1, which corresponds to U.S. Publication No. 2005115316, proposes integrating at least two sensors that are spaced apart from one another on or directly in the gun barrel. As the shell passes through, the sensors experience an expansion due to the gas pressure at the shell base; this expansion is converted into an electrical signal and is delivered to a subsequent signal processing unit, after amplification if necessary. Preferably, quartz sensors in the form of length measuring pins are used, which are located either in a support ring on or around the gun barrel, or are located directly in the gun barrel. The quartz sensors have the great advantage that they can convert even the smallest pressure changes into signals, are themselves very robust, and can be integrated with precise fit, i.e. in firm, slip-proof contact with the gun barrel. Consequently, mechanical loads on the gun barrel have no effect on the measurement result of the indirect pressure measurement. Moreover, the sensors are not directly exposed to the gas pressure and are built into a solid structure that is additional to the existing housing.
In contrast, DE 10 2005 024 179 A1, which corresponds to U.S. Publication No. 2007074625, substantially avoids a direct measurement of the current muzzle velocity, since the real muzzle velocity is determined from information about the current flight velocity of the shell, i.e. is calculated back therefrom. The detonation time of the shell is then corrected on the basis of this current shell velocity with the aid of a detonation time preset for a default muzzle velocity, and is used as the current fuze timing. A microwave transmitter, preferably in the GHz range, is used to transmit this information to the shell; said transmitter transmits the current time setting, determined for example by a fire-control computer, to the shell or munition.
Another method is to operate the barrel as a circular waveguide and to measure the Doppler velocity of the projectile in the barrel, as can be read from EP 0 023 365 A2, which corresponds to U.S. Pat. No. 4,283,989. The frequency of the signal here is above the cutoff frequency of the waveguide mode in question. The electromagnetic wave that builds up in this case propagates in the barrel and is reflected from the projectile. In addition, there is a Doppler frequency shift that depends on the instantaneous velocity.
It is disadvantageous in this regard that two sensors must be arranged at a defined spacing. This design increases the length of the measurement device at the muzzle of the gun barrel. This can lead to instability of the entire weapon or cause problems when using subcaliber ammunition. The sabots that detach upon emergence from the gun barrel can damage the measurement device. Moreover, the sensors must be fastened directly in or on the gun barrel. In many cases, the supplier of the gun barrel and the supplier of the muzzle velocity measurement device are not the same. This has the result that mounting the sensors on or in the barrel is possible only under difficult conditions, or is even impossible. A muzzle velocity measurement device should function independently of the gun barrel used, without interfering with the gun barrel itself. Another disadvantage results from the fact that the measurements of the flight velocity and the programming of the detonation time outside the gun barrel by means of a microwave transmitter require a certain resistance to interference for the transmission of information between transmitter and shell. Interference from natural sources, as well as intentional interference from a jammer, can impede the measurement of the flight speed and the subsequent programming or even make it impossible. Moreover, modern “electronic warfare” methods can be used to detect the emissions of the transmitter by external methods and locate the position of the gun. The position of the gun is thus known to the enemy, who will initiate countermeasures to attack the gun. The maxim today is “See but remain unseen.” If the gun reveals its position by emissions, that gun is in great danger from efficient weapons systems. Moreover, certain requirements are placed on the stability of the oscillator in measuring the Doppler frequency shift. Vibrations arising from firing can change the instantaneous frequency of the transmitter and increase the effort required to accurately measure the frequency shift. Furthermore, the gun barrel acts as an open circular waveguide and can act as an antenna. This means that an external eavesdropping device can detect the emissions and determine the position of the gun.